1. Field of the Invention
The present invention relates to a torque transmitting apparatus which has a driving unit and a driven member and transmits driving torque of variable phase difference between the driving member and the driven member, and particularly, relates to a valve timing adjusting device for the air-intake and exhaust valves which changes the valve operation timing according to the engine condition.
2. Description of Related Art
Driving torque of an engine is transmitted to a valve timing adjusting device from the crank shaft of an engine through a timing belt, chain or gears to a timing pulley which is a driving member of the valve timing adjusting device. A ring gear is interposed between the timing pulley and a cam shaft (which is a driven member) of the valve timing adjusting device to transmit the driving torque to the cam shaft. The ring gear engages helical splines of the timing pulley and the cam shaft. When the ring gear is moved axially, the timing pulley rotates around the cam shaft to change the valve timings of the air intake valve and exhaust valve. Such device is disclosed in U.S. Pat. No. 4,811,698 (Japanese Patent Publication Hei 5-77842) and Japanese Unexamined Patent Publication Hei 6-42316 (U.S. Pat. No. 5,426,992 issued to the same assignee).
In the device disclosed in U.S. Pat. No. 4,811,698, a plurality of gears are connected by elastic members and installed between the timing pulley and the cam shaft.
In the device disclosed in Japanese Unexamined Patent Publication Hei 6-42316, a transmitting member is composed of a control member having a spline formed on an outer periphery within a partial circular range and arc-shaped gears disposed in the rest of the circumference, and is interposed between a driving member and a driven member. The control member and the gear are biased in the opposite directions by the elastic members.
The gears disclosed in the above publications are formed by dividing a single ring gear by a plane perpendicular to the gear axis or by a plane including the axis. They are connected by elastic members to bias one of the gears in one direction, thereby suppressing rattling noise due to backlash of the gears.
However, the above mentioned devices cannot suppress the rattling noise (due to the backlash of the gears) completely when the biased ring gear is further driven by an oil pressure member in the same direction as it is biased by the elastic member since the biasing force of the elastic member is overcome by the driving force, resulting in the backlash of the splines.
It is possible to suppress the backlash if the biasing force of the elastic member is increased. However, oil pressure has to be increased to move the ring gear in the opposite direction since frictional force of the splines increases.